1. Field of the Invention
The present invention relates to a composite comprising a core having end walls and continuous fibers which are oriented along the end walls.
The present invention further relates to a composite comprising a core having end walls and continuous fibers which are oriented along the end walls where the continuous fibers are placed in tension prior to or simultaneously to being secured to the core.
The present invention further relates to a composite wherein the continuous fibers are impregnated with resin before or simultaneously with being secured to the core.
The present invention also relates to methods of making such composites.
2. Description of Background Art
Many composite products exist that use lightweight cores and high strength skins to create structural panels or monocoque shapes. The core has traditionally been manufactured out of a variety of materials such as wood, plastic, foam, metal, card board and the like depending on its end use. In some cases, the core is manufactured as an open ended cellular pattern having end walls. The pattern may be, for example, a biaxial, circular, honeycomb or flat pattern. FIGS. 1, 2, 3 and 4 show various prior art core configurations including tubes structures, honeycomb structures, closed cell foam and corrugated paper, respectively. FIGS. 1, 2 and 4 show examples of open ended cores.
Fibers are typically placed on top of this core to add strength to the composite as is also well known in the art. Fibers have traditionally been made out of glass, carbon, metal, thermoplastic and other well known materials and may be impregnated within a resin to form a flexible or rigid mat for easier handling. The fibers have traditionally been oriented either randomly over the core or in an orderly arrangement form over the core. However, even in cases where the core has an open ended cellular pattern, there has never been an attempt to orient the fibers along the end walls.
FIGS. 5, 6 and 7 show various fiber and fiber mat configurations including a woven fabric, unidirectional continuous fibers and chopped fibers, respectively. FIG. 8 shows a sheet which may be secured to the core and is void of fibers.
Processes for assembling such prior art composites are also well known. The core and fibers or fiber mat may be layered either by hand, in a compression mold, or vacuum forming, for example. Alternatively, an injection molding process may be used wherein the fibers or fiber mat is inserted into a mold half prior to the core being manufactured.
The fibers or fiber mat may be secured to the core using a variety of methods such as heat from the molding process, added heat, or an adhesive.
In many cases, fiber mat is inserted into the mold as a flat sheet and, if the mold has a predetermined shape, the fibers in the fiber mat are formed to match the predetermined shape. Depending on the actual predetermined shape, some of the fibers may be stretched taught and some of the fibers may be bent or folded. Fibers add the most strength and rigidity to the composite when placed in tension.
In other cases, the fiber mat and/or the core may be preformed to match the mold surface. Sometimes care is taken to ensure that the fibers composing the mat are made to be taut during this performing process.
While in general, composite materials are stronger and/or lighter than their traditional counterparts, there exists opportunity for further optimization. In many examples, the fibers are merely chopped and placed in the fiber mat. To increase the strength of the composite, either more fibers or more resin are added to the fiber mat or the core is strengthened.
In cases where a fibrous cloth or an ordinary arrangement of the fibers are placed over an open ended cellular core having end walls, the fibers randomly overlay and intersect the end walls. Further, when such a composite is placed under a bending force, the fibers may interrupt the visible surface of the composite between the end walls of the core, and at that location they create a failure in its ability to carry a load. To combat this failure propagation, resin or fiber thickness of the skin is increased.
Sometimes panel loads are relatively low and hence the weight of the composite is a primary objective. Attempts to keep the core and wall spacing wide and the skin thickness thin are negated by the fiber deflection and buckling when they are not supported by an end wall.
Accordingly, a need exists for an optimized composite design that can yield better strength and/or weight.